1. Field of the Invention
One embodiment of the disclosed invention relates to photoelectric conversion devices and manufacturing methods thereof.
2. Description of the Related Art
A solar cell can be given as one of photoelectric conversion elements for directly converting light received into electric power by a photovoltaic effect and outputting the electric power (see Reference 1). Unlike a conventional method for generating electric power, in a solar cell, energy conversion into heat energy or kinetic energy is not necessary in the middle of power generation.
The output of a solar cell varies according to the amount of solar radiation, temperature, operating-point voltage, or the like. Thus, it is preferable that the load of the solar cell be adjusted and maximum electric power be always taken out from the solar cell. For this reason, an electric power conversion element is connected to the solar cell and operation for taking out the maximum electric power from the solar cell (i.e., maximum power point tracking (MPPT)) is performed by the electric power conversion element.
Maximum power point tracking (MPPT) is operation by which the desired voltage level of a solar cell is set by detection of voltage or current at the operating point of the solar cell and the output of an electric power conversion element is adjusted so that a detected voltage level and the desired voltage level agree with each other. That is, by changes in the voltage of the solar cell and detection of a current value with respect to each voltage level, the output electric power of the solar cell is calculated from the product of the voltage level and the current value. Then, the output electric power of the solar cell is controlled so as to be maximum with a voltage level at which maximum electric power is obtained used as a desired voltage level (see Reference 2).